A lithium-ion battery has a configuration including a positive electrode containing an active material lithium transition metal oxide, a negative electrode containing active material carbon, an electrolytic solution containing an organic solvent dissolving a lithium salt, and a separator disposed between the positive electrode and the negative electrode.
The electrodes of a lithium-ion battery have a risk of contamination by metal foreign objects such as iron, copper, zinc, tin, cobalt, nickel, and chromium. Such contaminating metal foreign objects have a possibility of entering the battery in the form of a solid or ions. The contaminating metal foreign objects may cause an output voltage drop, or heat or fire defects in the lithium-ion battery. Particularly, when entry of metal foreign objects occurs in the vicinity of the positive electrode, the metal foreign objects become ionized under an inner electric field, and induced to the negative electrode side. Such ions precipitate on the negative electrode, and form dendrites, which grow and reach the positive electrode from the negative electrode, and short the positive and negative electrodes. Such shorting causes an OCV (Open Circuit Voltage) failure involving an output voltage drop, and, even worse, heat or fire defects.
In order to reduce such defects due to metal foreign objects, it has been proposed to handle a lithium-ion battery in a configuration in which the positive and negative electrodes are in contact with a coating separator. With such a structure, there will be no gap between the electrodes and the separator, and contaminating metal foreign objects do not come into contact with the electrodes during assembly, making it difficult for dendrites to occur from metal foreign objects (see, for example, JP-A-2013-127857).